Flame retardant covercoats for printed wiring should be solder resistant with good electrical resistance, and advantageously are also flexible to be adaptable to flexible printed circuits. For many applications it is useful for the coating to be photosensitive and thereby curable and/or patternable by U.V. radiation, preferably in an air atmosphere.
This invention is a coating material with these properties. It is based on dichloropropyl acrylate, selectively or non-selectively crosslinked to give a stable coating. The crosslinking agent may be any suitable material that produces a flexible polymer. The basic coating material, polymerized dichloropropyl acrylate (DCPA) is sufficiently flame retardant in itself that it is not essential that the crosslinking agent be non-burning. This allows considerable latitude in the selection. We have found that excellent coatings can be produced using a difunctional acrylate, and specifically neopentyl glycol diacrylate (NPGDA). A ratio of DCPA to NPGDA in the range of 2:1 to 6:1 will give useful coatings.